Edge chamfering methods

ABSTRACT

Processes of chamfering and/or beveling an edge of a glass or other substrate of arbitrary shape using lasers are described herein. Three general methods to produce chamfers on glass substrates are disclosed. The first method involves cutting the edge with the desired chamfer shape utilizing an ultra-short pulse laser. Treatment with the ultra-short laser may be optionally followed by a CO 2  laser for fully automated separation. The second method is based on thermal stress peeling of a sharp edge corner, and it has been demonstrated to work with different combination of an ultrashort pulse and/or CO 2  lasers. A third method relies on stresses induced by ion exchange to effect separation of material along a fault line produced by an ultra-short laser to form a chamfered edge of desired shape.

This application is a divisional of U.S. patent application Ser. No.14/530,410 filed Oct. 31, 2014, which claims the benefit of U.S.Provisional Application No. 61/917,213 filed on Dec. 17, 2013 as well asthe benefit of U.S. Provisional Application No. 62/022,885 filed on Jul.10, 2014 the entire disclosures of which are incorporated herein byreference.

BACKGROUND

In all cases where glass panels are cut for applications inarchitectural, automotive, consumer electronics, to mention a few areas,there will be edges, which will very likely require attention. There areas many different methods to cut and separate glass as there are edgeshapes. Glass can be cut mechanically (CNC machining, abrasive waterjet,scribing and breaking, etc), using electro-magnetic radiation (lasers,electrical discharges, gyrotron, etc) and many other methods. The moretraditional and common methods (scribe and break or CNC machining)create edges that are populated with different types and sizes ofdefects. It is also common to find that the edges are not perfectlyperpendicular to the surfaces. In order to eliminate the defects andgive the edges a more even surface with improved strength, they areusually ground. The grinding process involves abrasive removal of edgematerial that can give it the desired finishing and also shape its form(bull nosed, chamfered, pencil shape, etc). In order to allow thegrinding and polishing steps, it is necessary to cut parts that arelarger than the final desired dimensions.

While it is well known and understood that eliminating defects willincrease edge strength, there is not an agreement on the impact thatshape has on edge strength. The confusion occurs mainly because it iswell known that shape helps to increase damage resistance to impact andhandling of the edges. The fact is that edge shape really does notdetermine edge strength as defined by resistance to flexural (orbending) forces, but the defects size and distribution do have a greatimpact. However, a shaped edge does help to improve impact resistance bycreating smaller cross section and containing defects. For example, anedge with a straight face that is perpendicular to both surfacesaccumulates stress at these right angled corners that will chip andbreak when it is impacted by another object. Because of the accumulatedstress, the size of defects can be pretty big, which will diminish thestrength of that edge considerably. On the other hand, due to itssmoother shape, a rounded “bull-nosed” shaped edge will have loweraccumulated stress and smaller cross section which helps to reduce thesize and penetration of defects into the volume of the edge. Therefore,after an impact, a shaped edge should have higher “bending” strengththan a flat edge.

For the reasons discussed above, it is often desirable to have the edgesshaped, as opposed to flat and perpendicular to the surfaces. Oneimportant aspect of these mechanical cutting and edge shaping methods isthe degree of maintenance of the machines. Both for cutting andgrinding, old and worn down cutting heads or grinding rolls can producedamage which can significantly affect the strength of the edges, even ifthe naked eye cannot be see the differences. Other issues withmechanical cutting and grinding methods is that they are very laborintensive and require many grinding and polishing steps until the finaldesired finish, which generate a lot of debris and require cleaningsteps to avoid introduction of damages to the surfaces.

From process development and cost perspectives there are manyopportunities for improvement in cutting and chamfering edges of glasssubstrates. It is of great interest to have a faster, cleaner, cheaper,more repeatable and more reliable method of creating shaped edges thanwhat is currently practiced in the market today. Among severalalternative technologies, laser and other thermal sources have beentried and demonstrated to create shaped edges.

In general, ablative laser techniques tend to be slow due to the lowmaterial removal rate and they also generate a lot of debris and heataffected zones that lead to residual stress and micro-cracks. For thesame reason, melting and reshaping of the edges are also plagued with alot of deformation and accumulated thermal stress that can peel thatprocessed area. Finally, for the thermal peeling or crack propagatingtechniques, one of the main issues encountered is that the peeling isnot continuous.

Subsurface damage, or the small microcracks and material modificationcaused by any cutting process, is a concern for the edge strength ofglass or other brittle materials. Mechanical and ablative laserprocesses are particularly problematic with regard to subsurface damage.Edges cut with these processes typically require a lot of post-cutgrinding and polish to remove the subsurface damage layer, therebyincreasing edge strength to performance level required for applicationssuch as in consumer electronics.

SUMMARY

According to embodiments described herein, processes of chamferingand/or beveling an edge of a glass substrate of arbitrary shape usinglasers are presented. One embodiment involves cutting the edge with thedesired chamfer shape utilizing an ultra-short pulse laser that may beoptionally followed by a CO₂ laser for fully automated separation.Another embodiment involves thermal stress peeling of a sharp edgecorner with different combination of an ultrashort pulse and/or CO₂lasers. Another embodiment includes cutting the glass substrate by anycutting method, such as utilizing the ultra-short pulse laser, followedby chamfering solely by the use of a CO₂ laser.

In one embodiment, a method of laser processing a material includesfocusing a pulsed laser beam into a laser beam focal line and directingthe laser beam focal line into the material at a first angle ofincidence to the material, the laser beam focal line generating aninduced absorption within the material, the induced absorption producinga defect line along the laser beam focal line within the material. Themethod also includes translating the material and the laser beamrelative to each other, thereby forming a plurality of defect linesalong a first plane at the first angle within the material, anddirecting the laser beam focal line into the material at a second angleof incidence to the material, the laser beam focal line generating aninduced absorption within the material, the induced absorption producinga defect line along the laser beam focal line within the material. Themethod further includes translating the material or the laser beamrelative to one another, thereby forming a plurality of defect linesalong a second plane at the second angle within the material, the secondplane intersecting the first plane.

According to another embodiment, a method of laser processing a materialincludes focusing a pulsed laser beam into a laser beam focal line, andforming a plurality of defect lines along each of N planes within thematerial. The method also includes directing the laser beam focal lineinto the material at a corresponding angle of incidence to the material,the laser beam focal line generating an induced absorption within thematerial, the induced absorption producing a defect line along the laserbeam focal line within the material. The method further includestranslating the material and the laser beam relative to each other,thereby forming the plurality of defect lines along the correspondingplane of the N planes.

According to yet another embodiment, a method of laser processing aworkpiece includes focusing a pulsed laser beam into a laser beam focalline directed into the workpiece at an angle of incidence to theworkpiece, the angle intersecting an edge of the workpiece, the laserbeam focal line generating an induced absorption within the workpiece,and the induced absorption producing a defect line along the laser beamfocal line within the workpiece. The method also includes translatingthe workpiece and the laser beam relative to each other, thereby forminga plurality of defect lines along a plane at the angle within theworkpiece, and separating the workpiece along the plane by applying anion-exchange process to the workpiece.

In still another embodiment, a method of laser processing a materialincludes focusing a pulsed laser beam into a laser beam focal linedirected into the material, the laser beam focal line generating aninduced absorption within the material, and the induced absorptionproducing a defect line along the laser beam focal line within thematerial. The method also includes translating the material and thelaser beam relative to each other along a contour, thereby forming aplurality of defect lines along the contour within the material to tracea part to be separated, and separating the part from the material. Themethod further includes directing a focused infrared laser into the partalong a line adjacent an edge at a first surface of the part to peel afirst strip that defines a first chamfered edge, and directing thefocused infrared laser into the part along a line adjacent the edge at asecond surface of the part to peel a second strip that defines a secondchamfered edge.

The present disclosure extends to:

-   A method of laser processing comprising:    -   focusing a pulsed laser beam into a laser beam focal line;    -   directing the laser beam focal line into a material at a first        angle of incidence to the material, the laser beam focal line        generating an induced absorption within the material, the        induced absorption producing a defect line along the laser beam        focal line within the material;    -   translating the material and the laser beam relative to each        other, thereby forming a plurality of defect lines along a first        plane at the first angle within the material;    -   directing the laser beam focal line into the material at a        second angle of incidence to the material, the laser beam focal        line generating an induced absorption within the material, the        induced absorption producing a defect line along the laser beam        focal line within the material; and        translating the material or the laser beam relative to one        another, thereby forming a plurality of defect lines along a        second plane at the second angle within the material, the second        plane intersecting the first plane.

The present disclosure extends to:

A method of laser processing a material comprising:

-   -   focusing a pulsed laser beam into a laser beam focal line;    -   forming a plurality of defect lines along each of N planes        within the material, the forming plurality of defect lines        including:    -   (a) directing the laser beam focal line into the material at an        angle of incidence to the material corresponding to one of the N        planes, the laser beam focal line generating an induced        absorption within the material, the induced absorption producing        a defect line along the laser beam focal line within the        material;    -   (b) translating the material and the laser beam relative to each        other, thereby forming the plurality of defect lines along the        one of the N planes; and (c) repeating (a) and (b) for each of        the N planes.

The present disclosure extends to:

-   A method of laser processing a workpiece comprising:    -   focusing a pulsed laser beam into a laser beam focal line;    -   directing the laser beam focal line into the workpiece at an        angle of incidence to the workpiece, the angle of incidence        intersecting an edge of the workpiece, the laser beam focal line        generating an induced absorption within the workpiece, the        induced absorption producing a defect line along the laser beam        focal line within the workpiece;    -   translating the workpiece and the laser beam relative to each        other, thereby forming a plurality of defect lines along a plane        at the angle within the workpiece; and        separating the workpiece along the plane by subjecting the        workpiece to an ion-exchange process.

The present disclosure extends to:

-   A method of laser processing a material comprising:    -   focusing a pulsed laser beam into a laser beam focal line;    -   directing the laser beam focal line into a material, the laser        beam focal line generating an induced absorption within the        material, the induced absorption producing a defect line along        the laser beam focal line within the material;    -   translating the material and the laser beam relative to each        other along a contour, thereby forming a plurality of defect        lines along the contour within the material, the contour tracing        the perimeter of a part to be separated from the material;    -   separating the part from the material;    -   directing a focused infrared laser into the separated part along        a line adjacent an edge at a first surface of the part to peel a        first strip that defines a first chamfered edge of the separated        part; and        directing the focused infrared laser into the separated part        along a line adjacent the edge at a second surface of the part        to peel a second strip that defines a second chamfered edge of        the separated part.

The present disclosure extends to:

-   -   A glass article including at least one chamfered edge having a        plurality of defect lines extending at least 250 μm, the defect        lines each having a diameter less than or equal to about 5 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the disclosure, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present disclosure.

FIGS. 1A-1C are illustrations of a fault line with equally spaced defectlines of modified glass.

FIGS. 2A and 2B are illustrations of positioning of the laser beam focalline, i.e., the processing of a material transparent for the laserwavelength due to the induced absorption along the focal line.

FIG. 3A is an illustration of an optical assembly for laser drillingaccording.

FIGS. 3B-1-3B-4 are an illustration of various possibilities to processthe substrate by differently positioning the laser beam focal linerelative to the substrate.

FIG. 4 is an illustration of a second optical assembly for laserdrilling.

FIGS. 5A and 5B are illustrations of a third optical assembly for laserdrilling.

FIG. 6 is a schematic illustration of a fourth optical assembly forlaser drilling.

FIG. 7A is a flow chart of the various methods described in the presentapplication to form a more robust edge—creating chamfers and sacrificialedges.

FIG. 7B illustrates a process of creating a chamfered edge with defectlines.

FIG. 7C illustrates laser chamfering of glass edges using a focused andangled ultrashort laser that generates defect lines along pre-determinedplanes. Top shows an example using 3 defect line planes compared to justtwo for the bottom images.

FIGS. 8A and 8B depict laser emission as a function of time for apicosecond laser. Each emission is characterized by a pulse “burst”which may contain one or more sub-pulses. Times corresponding to pulseduration, separation between pulses, and separation between bursts areillustrated.

FIG. 9 is an illustration of a thermal gradient created by the focusedlaser that is highly absorbed by the glass. The cracking line is betweenthe strain and softening zones.

FIG. 10 illustrates edge chamfering by thermal peeling.

FIG. 11A is an illustration of edge chamfering process using defectlines and then thermal peeling. First, the picosecond laser is focusedat an angle and a defect line is created on an angled plane. Then afocused CO₂ laser is scanned next to the defect line, at a controlledlateral offset. A strip of glass is peeled from that corner and forms achamfer.

FIG. 11B illustrates, as shown in the side view of the edge, that thestrip of glass formed by the process shown in FIG. 11A does notnecessarily peel entirely along the defect line plane.

FIG. 12 is an illustration of edge chamfer changes with peeling speedusing only a focused CO₂ laser. All other CO₂ laser parameters were keptthe same.

FIG. 13 illustrates using defect lines which remain after the cut partis released to serve as sacrificial regions, arresting the propagationof cracks caused by impact to the edges of the part.

FIG. 14A is an illustration of a cut part with internal defect linesbeing placed into ion-exchange, which adds enough stress to remove theperforated edges and form the desired edge chamfer.

FIG. 14B is the use of ion exchange (IOX) to release chamfered corners,similar to the illustration shown in FIG. 14A, but with only two defectline planes.

FIG. 14C is an illustration of a chamfer with many angles (more than 3defect line planes).

DETAILED DESCRIPTION

A description of exemplary embodiments follows.

Embodiments described herein relate to processes of chamfering and/orbeveling an edge of a glass substrate and other substantiallytransparent materials of arbitrary shape using lasers. Within thecontext of the present disclosure, a material is substantiallytransparent to the laser wavelength when the absorption is less thanabout 10%, preferably less than about 1% per mm of material depth atthis wavelength. A first embodiment involves cutting the edge with thedesired chamfer shape utilizing an ultra-short pulse laser that may beoptionally followed by an infrared (e.g., CO₂) laser for fully automatedseparation. A second embodiment involves thermal stress peeling of asharp edge corner with different combinations of an ultrashort pulseand/or CO₂ lasers. Another embodiment includes cutting the glasssubstrate by any cutting method, such as utilizing the ultra-short pulselaser, followed by chamfering solely by the use of a CO₂ laser to workwith different combinations of an ultrashort pulse and/or CO₂ lasers.

In the first method, the process fundamental step is to create faultlines on intersecting planes that delineate the desired edge shape andestablish a path of least resistance for crack propagation and henceseparation and detachment of the shape from its substrate matrix. Thismethod essentially creates the shaped edge while cutting the part out ofthe main substrate. The laser separation method can be tuned andconfigured to enable manual separation, partial separation, orself-separation of the shaped edges out of the original substrate. Theunderlying principle to generate these fault lines is described indetail below and in U.S. Application No. 61/752,489 filed on Jan. 15,2013, the entire contents of which are incorporated herein by referenceas if fully set forth herein.

In the first step, the object to be processed is irradiated with anultra-short pulsed laser beam that is condensed into a high aspect ratioline focus that penetrates through the thickness of the substrate.Within this volume of high energy density the material is modified vianonlinear effects. It is important to note that without this highoptical intensity, nonlinear absorption is not triggered. Below thisintensity threshold, the material is transparent to the laser radiationand remains in its original state.

The selection of the laser source is predicated on the ability to inducemulti-photon absorption (MPA) in the transparent material. MPA is thesimultaneous absorption of multiple photons of identical or differentfrequencies in order to excite a material from a lower energy state(usually the ground state) to a higher energy state (excited state). Theexcited state may be an excited electronic state or an ionized state.The energy difference between the higher and lower energy states of thematerial is equal to the sum of the energies of the two or more photons.MPA is a nonlinear process that is generally several orders of magnitudeweaker than linear absorption. It differs from linear absorption in thatthe strength of MPA depends on the square or higher power of the lightintensity, thus making it a nonlinear optical process. At ordinary lightintensities, MPA is negligible. If the light intensity (energy density)is extremely high, such as in the region of focus of a laser source(particularly a pulsed laser source), MPA becomes appreciable and leadsto measurable effects in the material within the region where the energydensity of the light source is sufficiently high. Within the focalregion, the energy density may be sufficiently high to result inionization.

At the atomic level, the ionization of individual atoms has discreteenergy requirements. Several elements commonly used in glass (e.g., Si,Na, K) have relatively low ionization energies (˜5 eV). Without thephenomenon of MPA, a wavelength of about 248 nm would be required tocreate linear ionization at ˜5 eV. With MPA, ionization or excitationbetween states separated in energy by ˜5 eV can be accomplished withwavelengths longer than 248 nm. For example, photons with a wavelengthof 532 nm have an energy of ˜2.33 eV, so two photons with wavelength 532nm can induce a transition between states separated in energy by ˜4.66eV in two-photon absorption (TPA), for example. Thus, atoms and bondscan be selectively excited or ionized in the regions of a material wherethe energy density of the laser beam is sufficiently high to inducenonlinear TPA of a laser wavelength having half the required excitationenergy, for example.

MPA can result in a local reconfiguration and separation of the excitedatoms or bonds from adjacent atoms or bonds. The resulting modificationin the bonding or configuration can result in non-thermal ablation andremoval of matter from the region of the material in which MPA occurs.This removal of matter creates a structural defect (e.g. a defect line,damage line, or “perforation”) that mechanically weakens the materialand renders it more susceptible to cracking or fracturing uponapplication of mechanical or thermal stress. By controlling theplacement of perforations, a contour or path along which cracking occurscan be precisely defined and precise micromachining of the material canbe accomplished. The contour defined by a series of perforations may beregarded as a fault line and corresponds to a region of structuralweakness in the material. In one embodiment, micromachining includesseparation of a part from the material processed by the laser, where thepart has a precisely defined shape or perimeter determined by a closedcontour of perforations formed through MPA effects induced by the laser.As used herein, the term closed contour refers to a perforation pathformed by the laser line, where the path intersects with itself at somelocation. An internal contour is a path formed where the resulting shapeis entirely surrounded by an outer portion of material.

The laser is ultrashort pulsed laser (pulse durations on the order tensof picoseconds or shorter) and can be operated in pulse mode or burstmode. In pulse mode, a series of nominally identical single pulses isemitted from the laser and directed to the workpiece. In pulse mode, therepetition rate of the laser is determined by the spacing in timebetween the pulses. In burst mode, bursts of pulses are emitted from thelaser, where each burst includes two or more pulses (of equal ordifferent amplitude). In burst mode, pulses within a burst are separatedby a first time interval (which defines a pulse repetition rate for theburst) and the bursts are separated by a second time interval (whichdefines a burst repetition rate), where the second time interval istypically much longer than the first time interval. As used herein(whether in the context of pulse mode or burst mode), time intervalrefers to the time difference between corresponding parts of a pulse orburst (e.g. leading edge-to-leading edge, peak-to-peak, or trailingedge-to-trailing edge). Pulse and burst repetition rates are controlledby the design of the laser and can typically be adjusted, within limits,by adjusting operating conditions of the laser. Typical pulse and burstrepetition rates are in the kHz to MHz range.

The laser pulse duration (in pulse mode or for pulses within a burst inburst mode) may be 10⁻¹⁰ s or less, or 10⁻¹¹ s or less, or 10⁻¹² s orless, or 10⁻¹³ s or less. In the exemplary embodiments described herein,the laser pulse duration is greater than 10⁻¹⁵.

The perforations may be spaced apart and precisely positioned bycontrolling the velocity of a substrate or stack relative to the laserthrough control of the motion of the laser and/or the substrate orstack. As an example, in a thin transparent substrate moving at 200mm/sec exposed to a 100 kHz series of pulses (or bursts of pulses), theindividual pulses would be spaced 2 microns apart to create a series ofperforations separated by 2 microns. This defect line (perforation)spacing is sufficiently close to allow for mechanical or thermalseparation along the contour defined by the series of perforations.

FIGS. 1A-1C illustrate that a method to cut and separate a substratematerial (e.g., sapphire or glass) can be essentially based on creatinga fault line 110 formed of a plurality of vertical defect lines 120 inthe substrate material 130 with an ultra-short pulsed laser 140.Depending on the material properties (absorption, CTE, stress,composition, etc) and laser parameters chosen for processing thematerial 130, the creation of a fault line 110 alone can be enough toinduce self-separation. In this case, no secondary separation processes,such as tension/bending forces, heating, or CO₂ laser, are necessary.Distance between adjacent defect lines 120 along the direction of thefault lines 110 can, for example, be in the range from 0.25 μm to 50 μm,or in the range from 0.50 μm to about 20 μm, or in the range from 0.50μm to about 15 μm, or in the range from 0.50 μm to 10 μm, or in therange from 0.50 μm to 3.0 μm or in the range from 3.0 μm to 10 μm.

By scanning the laser over a particular path or contour, a series ofperforations is created (a few microns wide) that defines the perimeteror shape of the part to be separated from the substrate. The series ofperforations may also be referred to herein as a fault line. Theparticular laser method used (described below) has the advantage that ina single pass, it creates highly controlled perforation through thematerial, with extremely little (<75 μm, often <50 μm) subsurface damageand debris generation. This is in contrast to the typical use ofspot-focused laser to ablate material, where multiple passes are oftennecessary to completely perforate the glass thickness, large amounts ofdebris are formed from the ablation process, and more extensivesub-surface damage (>100 μm) and edge chipping occur. As used herein,subsurface damage refers to the maximum size (e.g. length, width,diameter) of structural imperfections in the perimeter surface of thepart separated from the substrate or material subjected to laserprocessing in accordance with the present disclosure. Since thestructural imperfections extend from the perimeter surface, subsurfacedamage may also be regarded as the maximum depth from the perimetersurface in which damage from laser processing in accordance with thepresent disclosure occurs. The perimeter surface of the separated partmay be referred to herein as the edge or the edge surface of theseparated part. The structural imperfections may be cracks or voids andrepresent points of mechanical weakness that promote fracture or failureof the part separated from the substrate or material. By minimizing thesize of subsurface damage, the present method improves the structuralintegrity and mechanical strength of separated parts.

In some cases, the created fault line is not enough to separate the partfrom the substrate spontaneously and a secondary step may be necessary.If so desired, a second laser can be used to create thermal stress toseparate it. Separation can be achieved after the creation of a faultline, for example, by application of mechanical force or by using athermal source (e.g. an infrared laser, for example a CO₂ laser) tocreate thermal stress and force the part to separate from the substrate.Another option is to have the CO₂ laser only start the separation andthen finish the separation manually. The optional CO₂ laser separationis achieved, for example, with a defocused cw laser emitting at 10.6 μmand with power adjusted by controlling its duty cycle. Focus change(i.e., extent of defocusing up to and including focused spot size) isused to vary the induced thermal stress by varying the spot size.Defocused laser beams include those laser beams that produce a spot sizelarger than a minimum, diffraction-limited spot size on the order of thesize of the laser wavelength. For example, defocused spot sizes (1/e²diameter) of about 2 to 12 mm, or 7 mm, 2 mm and 20 mm can be used forCO₂ lasers, for example, whose diffraction-limited spot size is muchsmaller given the emission wavelength of 10.6 μm. The power density ofthe cw laser is controlled or selected to provide a relatively lowintensity beam, such that laser spot heats the surface of the substratematerial to create thermal stress without ablation and without inducingformation of cracks that deviate substantially from the plane containingthe defect lines. The length of cracks deviating from the defect linesis less than 20 μm, or less than 5 μm, or less than 1 μm.

There are several methods to create the defect line. The optical methodof forming the line focus can take multiple forms, using donut shapedlaser beams and spherical lenses, axicon lenses, diffractive elements,or other methods to form the linear region of high intensity. The typeof laser (picosecond, femtosecond, etc.) and wavelength (IR, green, UV,etc.) can also be varied, as long as sufficient optical intensities arereached in the region of focus to create breakdown of the substratematerial through nonlinear optical effects. Substrate materials includeglass, glass laminates, glass composites, sapphire, glass-sapphirestacks, and other materials that are substantially transparent to thewavelength of the laser. A sapphire layer can be bonded onto a glasssubstrate, for example. Glass substrates can include high-performanceglass such as Corning's Eagle X6®, or inexpensive glass such assoda-lime glass, for example.

In the present application, an ultra-short pulsed laser is used tocreate a high aspect ratio vertical defect line in a consistent,controllable and repeatable manner. The details of the optical setupthat enables the creation of this vertical defect line are describedbelow, and in U.S. Application No. 61/752,489 filed on Jan. 15, 2013,which is also referenced above, and the entire contents of which areincorporated by reference as if fully set forth herein. The essence ofthis concept is to use an axicon lens element in an optical lensassembly to create a region of high aspect ratio, taper-freemicrochannels using ultra-short (picoseconds or femtosecond duration)Bessel beams. In other words, the axicon condenses the laser beam into ahigh intensity region of cylindrical shape and high aspect ratio (longlength and small diameter) in the substrate material. Due to the highintensity created with the condensed laser beam, nonlinear interactionof the electromagnetic field of the laser and the substrate materialoccurs and the laser energy is transferred to the substrate to effectformation of defects that become constituents of the fault line.However, it is important to realize that in the areas of the materialwhere the laser energy intensity is not high (e.g., substrate surface,volume of substrate surrounding the central convergence line), thematerial is transparent to the laser and there is no mechanism fortransferring energy from the laser to the material. As a result, nothinghappens to the substrate when the laser intensity is below the nonlinearthreshold.

As described above, it is possible to create microscopic (e.g., <0.5 μmand >100 nm in diameter or <2 μm and >100 nm in diameter) elongateddefect lines (also referred to herein as perforations or damage tracks)in a transparent material using one or more high energy pulses or one ormore bursts of high energy pulses. The perforations represent regions ofthe substrate material modified by the laser. The laser-inducedmodifications disrupt the structure of the substrate material andconstitute sites of mechanical weakness. Structural disruptions includecompaction, melting, dislodging of material, rearrangements, and bondscission. The perforations extend into the interior of the substratematerial and have a cross-sectional shape consistent with thecross-sectional shape of the laser (generally circular). The averagediameter of the perforations may be in the range from 0.1 μm to 50 μm,or in the range from 1 μm to 20 μm, or in the range from 2 μm to 10 μm,or in the range from 0.1 μm to 5 μm. In some embodiments, theperforation is a “through hole”, which is a hole or an open channel thatextends from the top to the bottom of the substrate material. In someembodiments, the perforation may not be a continuously open channel andmay include sections of solid material dislodged from the substratematerial by the laser. The dislodged material blocks or partially blocksthe space defined by the perforation. One or more open channels(unblocked regions) may be dispersed between sections of dislodgedmaterial. The diameter of the open channels is may be <1000 nm, or <500nm, or <400 nm, or <300 nm or in the range from 10 nm to 750 nm, or inthe range from 100 nm to 500 nm. The disrupted or modified area (e.g,compacted, melted, or otherwise changed) of the material surrounding theholes in the embodiments disclosed herein, preferably has diameter of<50 μm (e.g, <10 μm).

The individual perforations can be created at rates of several hundredkilohertz (several hundred thousand perforations per second, forexample). Thus, with relative motion between the laser source and thematerial these perforations can be placed adjacent to one another(spatial separation varying from sub-micron to several microns or eventens of microns as desired). This spatial separation is selected inorder to facilitate cutting.

Turning to FIGS. 2A and 2B, a method of laser drilling a materialincludes focusing a pulsed laser beam 2 into a laser beam focal line 2b, viewed along the beam propagation direction. Laser beam focal line 2b can be created by several ways, for example, Bessel beams, Airy beams,Weber beams and Mathieu beams (i.e, non-diffractive beams), whose fieldprofiles are typically given by special functions that decay more slowlyin the transverse direction (i.e. direction of propagation) than theGaussian function. As shown in FIG. 3A, laser 3 (not shown) emits laserbeam 2, at the beam incidence side of the optical assembly 6 referred toas 2 a, which is incident onto the optical assembly 6. The opticalassembly 6 turns the incident laser beam into a laser beam focal line 2b on the output side over a defined expansion range along the beamdirection (length l of the focal line). The planar substrate 1 to beprocessed is positioned in the beam path after the optical assemblyoverlapping at least partially the laser beam focal line 2 b of laserbeam 2. Reference 1 a designates the surface of the planar substratefacing the optical assembly 6 or the laser, respectively, and reference1 b designates the reverse surface of substrate 1 (the surface remote,or further away from, optical assembly 6 or the laser). The substratethickness (measured perpendicularly to the planes 1 a and 1 b, i.e., tothe substrate plane) is labeled with d.

As FIG. 2A depicts, substrate 1 is aligned substantially perpendicularlyto the longitudinal beam axis and thus behind the same focal line 2 bproduced by the optical assembly 6 (the substrate is perpendicular tothe drawing plane) and viewed along the beam direction it is positionedrelative to the focal line 2 b in such a way that the focal line 2 bviewed in beam direction starts before the surface 1 a of the substrateand stops before the surface 1 b of the substrate, i.e. still within thesubstrate. In the overlapping area of the laser beam focal line 2 b withsubstrate 1, i.e. in the substrate material covered by focal line 2 b,the laser beam focal line 2 b thus generates (in case of a suitablelaser intensity along the laser beam focal line 2 b which intensity isensured due to the focusing of laser beam 2 on a section of length l,i.e. a line focus of length l) a section 2 c aligned with thelongitudinal beam direction, along which an induced nonlinear absorptionis generated in the substrate material. Such line focus can be createdby several ways, for example, Bessel beams, Airy beams, Weber beams andMathieu beams (i.e, non-diffractive beams), whose field profiles aretypically given by special functions that decay more slowly in thetransverse direction (i.e. direction of propagation) than the Gaussianfunction. The induced nonlinear absorption induces defect line formationin the substrate material along section 2 c. The defect line formationis not only local, but extends over the entire length of section 2 c ofthe induced absorption. The length of section 2 c (which corresponds tothe length of the overlapping of laser beam focal line 2 b withsubstrate 1) is labeled with reference L. The average diameter or extentof the section of the induced absorption (or the sections in thematerial of substrate 1 undergoing the defect line formation) is labeledwith reference D. The average extension D basically corresponds to theaverage diameter 6 of the laser beam focal line 2 b, that is, an averagespot diameter in a range of between about 0.1 μm and about 5 μm.

As FIG. 2A shows, the substrate material (which is transparent for thewavelength λ of laser beam 2) is heated due to the induced absorptionalong the focal line 2 b. FIG. 2B illustrates that the heated substratematerial will eventually expand so that a corresponding induced tensionleads to micro-crack formation, with the tension being the highest atsurface 1 a.

Representative optical assemblies 6, which can be applied to generatethe focal line 2 b, as well as optical systems in which these opticalassemblies can be applied, are described below. All assemblies orsystems are based on the description above so that identical referencesare used for identical components or features or those which are equalin their function. Therefore only the differences are described below.

To ensure high quality (regarding breaking strength, geometricprecision, roughness and avoidance of re-machining requirements) of thesurface of the separated part along which separation occurs, theindividual focal lines positioned on the substrate surface along theline of separation (fault line) should be generated using the opticalassembly described below (hereinafter, the optical assembly isalternatively also referred to as laser optics). The roughness of theseparated surface (the perimeter surface of the separated part) resultsis determined primarily by the spot size or the spot diameter of thefocal line. Roughness of a surface can be characterized, for example, bythe Ra surface roughness parameter defined by the ASME B46.1 standard.As described in ASME B46.1, Ra is the arithmetic average of the absolutevalues of the surface profile height deviations from the mean line,recorded within the evaluation length. In alternative terms, Ra is theaverage of a set of absolute height deviations of individual features(peaks and valleys) of the surface relative to the mean.

In order to achieve a small spot size of, for example, 0.5 μm to 2 μmfor a given wavelength λ of the laser 3 that interacts with the materialof substrate 1), certain requirements must usually be imposed on thenumerical aperture of laser optics 6. These requirements are met bylaser optics 6 described below. In order to achieve the requirednumerical aperture, the optics must, on the one hand, dispose of therequired opening for a given focal length, according to the known Abbéformulae (N.A.=n sin (theta), n: refractive index of the glass to beprocesses, theta: half the aperture angle; and theta=arctan (D_(L)/2f);D_(L): aperture diameter, f: focal length). On the other hand, the laserbeam must illuminate the optics up to the required aperture, which istypically achieved by means of beam widening using widening telescopesbetween laser and focusing optics.

The spot size should not vary too strongly for the purpose of a uniforminteraction along the focal line. This can, for example, be ensured (seethe embodiment below) by illuminating the focusing optics only in asmall, circular area so that the beam opening and thus the percentage ofthe numerical aperture only vary slightly.

According to FIG. 3A (section perpendicular to the substrate plane atthe level of the central beam in the laser beam bundle of laserradiation 2; here, too, laser beam 2 is incident perpendicularly (beforeentering optical assembly 6) to the substrate plane, i.e. angle θ is 0°so that the focal line 2 b or the section of the induced absorption 2 cis parallel to the substrate normal), the laser radiation 2 a emitted bylaser 3 is first directed onto a circular aperture 8 which is completelyopaque for the laser radiation used. Aperture 8 is orientedperpendicular to the longitudinal beam axis and is centered on thecentral beam of the depicted beam bundle 2 a. The diameter of aperture 8is selected in such a way that the beam bundles near the center of beambundle 2 a or the central beam (here labeled with 2 aZ) hit the apertureand are completely absorbed by it. Only the beams in the outer perimeterrange of beam bundle 2 a (marginal rays, here labeled with 2 aR) are notabsorbed due to the reduced aperture size compared to the beam diameter,but pass aperture 8 laterally and hit the marginal areas of the focusingoptic elements of the optical assembly 6, which is designed as aspherically cut, bi-convex lens 7 in this embodiment.

Lens 7 centered on the central beam is deliberately designed as anon-corrected, bi-convex focusing lens in the form of a common,spherically cut lens. In this design embodiment, the sphericalaberration of such a lens is deliberately used. As an alternative,aspheres or multi-lens systems deviating from ideally corrected systems,which do not form an ideal focal point but a distinct, elongated focalline of a defined length, can also be used (i.e., lenses or systemswhich do not have a single focal point). The zones of the lens thusfocus along a focal line 2 b, subject to the distance from the lenscenter. The diameter of aperture 8 across the beam direction isapproximately 90% of the diameter of the beam bundle (beam bundlediameter defined by the extension to the decrease to 1/e²) andapproximately 75% of the diameter of the lens 7 of the optical assembly6. The focal line 2 b of a not aberration-corrected spherical lens 7generated by blocking out the beam bundles in the center is thus used.FIG. 3A shows the section in one plane through the central beam, thecomplete three-dimensional bundle can be seen when the depicted beamsare rotated around the focal line 2 b.

One potential disadvantage of this type of a focal line formed by lens 7and the system shown in FIG. 3A is that the conditions (spot size, laserintensity) along the focal line, and thus along the desired depth in thematerial, vary and that therefore the desired type of interaction (nomelting, induced absorption, thermal-plastic deformation up to crackformation) may possibly occur only in selected portions of the focalline. This means in turn that possibly only a part of the incident laserlight is absorbed in the desired way. In this way, the efficiency of theprocess (required average laser power for the desired separation speed)is impaired on the one hand, and on the other hand the laser light mightbe transmitted into undesired deeper places (parts or layers adherent tothe substrate or the substrate holding fixture) and interact there in anundesirable way (heating, diffusion, absorption, unwanted modification).

FIG. 3B-1-4 show (not only for the optical assembly in FIG. 3A, butbasically also for any other applicable optical assembly 6) that thelaser beam focal line 2 b can be positioned differently by suitablypositioning and/or aligning the optical assembly 6 relative to substrate1 as well as by suitably selecting the parameters of the opticalassembly 6. As FIG. 3B-1 outlines, the length l of the focal line 2 bcan be adjusted in such a way that it exceeds the substrate thickness d(here by factor 2). If substrate 1 is placed (viewed in longitudinalbeam direction) centrally to focal line 2 b, the section of inducedabsorption 2 c is generated over the entire substrate thickness. Thelaser beam focal line 2 b can have a length l in a range of betweenabout 0.1 mm and about 100 mm or in a range of between about 0.1 mm andabout 10 mm, or in a range of between about 0.1 mm and about 1 mm, forexample. Various embodiments can be configured to have length 1 of about0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.7 mm, 1 mm, 2 mm, 3 mm or 5mm, for example.

In the case shown in FIG. 3B-2, a focal line 2 b of length l isgenerated which corresponds more or less to the substrate extension d.As substrate 1 relative to line 2 is positioned in such a way that line2 b starts in a point before, i.e. outside the substrate, the length Lof the section of induced absorption 2 c (which extends here from thesubstrate surface to a defined substrate depth, but not to the reversesurface 1 b) is smaller than the length l of focal line 2 b. FIG. 3B-3shows the case in which the substrate 1 (viewed along the beamdirection) is positioned above the starting point of focal line 2 b sothat, as in FIG. 3B-2, the length l of line 2 b is greater than thelength L of the section of induced absorption 2 c in substrate 1. Thefocal line thus starts within the substrate and extends over the reverse(remote) surface 1 b to beyond the substrate. FIG. 3B-4 shows the casein which the focal line length l is smaller than the substrate thicknessd so that—in the case of a central positioning of the substrate relativeto the focal line viewed in the direction of incidence—the focal linestarts near the surface 1 a within the substrate and ends near thesurface 1 b within the substrate (1=0.75·d).

It is particularly advantageous to realize the focal line positioning insuch a way that at least one surface 1 a, 1 b is covered by the focalline, i.e. that the section of induced absorption 2 c starts at least onone surface. In this way it is possible to achieve virtually idealdrilling or cutting avoiding ablation, feathering and particulation atthe surface.

FIG. 4 depicts another applicable optical assembly 6. The basicconstruction follows the one described in FIG. 3A so that only thedifferences are described below. The depicted optical assembly is basedthe use of optics with a non-spherical free surface in order to generatethe focal line 2 b, which is shaped in such a way that a focal line ofdefined length 1 is formed. For this purpose, aspheres can be used asoptic elements of the optical assembly 6. In FIG. 4, for example, aso-called conical prism, also often referred to as axicon, is used. Anaxicon is a special, conically cut lens which forms a spot source on aline along the optical axis (or transforms a laser beam into a ring).The layout of such an axicon is principally known to one skilled in theart; the cone angle in the example is 10°. The apex of the axiconlabeled here with reference 9 is directed towards the incidencedirection and centered on the beam center. As the focal line 2 b of theaxicon 9 already starts in its interior, substrate 1 (here alignedperpendicularly to the main beam axis) can be positioned in the beampath directly behind axicon 9. As FIG. 4 shows, it is also possible toshift substrate 1 along the beam direction due to the opticalcharacteristics of the axicon while remaining within the range of focalline 2 b. The section of the induced absorption 2 c in the material ofsubstrate 1 therefore extends over the entire substrate depth d.

However, the depicted layout is subject to the following restrictions:Since the region of focal line 2 b formed by axicon 9 begins with axicon9, a significant part of the laser energy is not focused into thesection of induced absorption 2 c of focal line 2 b, which is locatedwithin the material, in the situation where there is a separationbetween axicon 9 and the material to be processed. Furthermore, length lof focal line 2 b is related to the beam diameter for the refractionindices and cone angles of axicon 9. This is why, in case of relativelythin materials (several millimeters), the total focal line is muchlonger than the thickness of the substrate, having the effect that thelaser energy is again not specifically focused into the material.

For this reason, it may be desirable to use an optical assembly 6 whichincludes both an axicon and a focusing lens. FIG. 5A depicts such anoptical assembly 6 in which a first optical element (viewed along thebeam direction) with a non-spherical free surface designed to form alaser beam focal line 2 b is positioned in the beam path of laser 3. Inthe case shown in FIG. 5A, this first optical element is an axicon 10with a cone angle of 5°, which is positioned perpendicularly to the beamdirection and centered on laser beam 3. The apex of the axicon isoriented towards the beam direction. A second, focusing optical element,here the plano-convex lens 11 (the curvature of which is orientedtowards the axicon), is positioned in beam direction at a distance Z1from the axicon 10. The distance Z1, in this case approximately 300 mm,is selected in such a way that the laser radiation formed by axicon 10circularly incident on the outer radial portion of lens 11. Lens 11focuses the circular radiation on the output side at a distance Z2, inthis case approximately 20 mm from lens 11, on a focal line 2 b of adefined length, in this case 1.5 mm. The effective focal length of lens11 is 25 mm in this embodiment. The circular transformation of the laserbeam by axicon 10 is labeled with the reference SR.

FIG. 5B depicts the formation of the focal line 2 b or the inducedabsorption 2 c in the material of substrate 1 according to FIG. 5A indetail. The optical characteristics of both elements 10, 11 as well astheir positioning is selected in such a way that the extension 1 of thefocal line 2 b in beam direction is exactly identical with the thicknessd of substrate 1. Consequently, an exact positioning of substrate 1along the beam direction is required in order to position the focal line2 b exactly between the two surfaces 1 a and 1 b of substrate 1, asshown in FIG. 5B.

It is therefore advantageous if the focal line is formed at a certaindistance from the laser optics, and if the greater part of the laserradiation is focused up to a desired end of the focal line. Asdescribed, this can be achieved by illuminating a primarily focusingelement 11 (lens) only circularly (annularly) on a required zone, which,on the one hand, serves to realize the required numerical aperture andthus the required spot size, on the other hand, however, the circle ofdiffusion diminishes in intensity after the required focal line 2 b overa very short distance in the center of the spot, as a basically circularspot is formed. In this way, the defect line formation is stopped withina short distance in the required substrate depth. A combination ofaxicon 10 and focusing lens 11 meets this requirement. The axicon actsin two different ways: due to the axicon 10, a usually round laser spotis sent to the focusing lens 11 in the form of a ring, and theasphericity of axicon 10 has the effect that a focal line is formedbeyond the focal plane of the lens instead of at a focal point in thefocal plane. The length l of focal line 2 b can be adjusted via the beamdiameter on the axicon. The numerical aperture along the focal line, onthe other hand, can be adjusted via the distance Z1 (axicon-lensseparation) and via the cone angle of the axicon. In this way, theentire laser energy can be concentrated in the focal line.

If the defect line formation is supposed to continue to the back side ofthe substrate, the circular (annular) illumination still has theadvantage that (1) the laser power is used optimally in the sense thatmost of the laser light remains concentrated in the required length ofthe focal line, and (2) it is possible to achieve a uniform spot sizealong the focal line—and thus a uniform separation process along thefocal line—due to the circularly illuminated zone in conjunction withthe desired aberration set by means of the other optical functions.

Instead of the plano-convex lens depicted in FIG. 5A, it is alsopossible to use a focusing meniscus lens or another higher correctedfocusing lens (asphere, multi-lens system).

In order to generate very short focal lines 2 b using the combination ofan axicon and a lens depicted in FIG. 5A, it would be necessary toselect a very small beam diameter of the laser beam incident on theaxicon. This has the practical disadvantage that the centering of thebeam onto the apex of the axicon must be very precise and that thereforethe result is very sensitive to directional variations of the laser(beam drift stability). Furthermore, a tightly collimated laser beam isvery divergent, i.e. due to the light deflection the beam bundle becomesblurred over short distances.

Turning to FIG. 6, both effects can be avoided by inserting anotherlens, a collimating lens 12 in the optical assembly 6. The additionalpositive lens 12 serves to adjust the circular illumination of focusinglens 11 very tightly. The focal length f of collimating lens 12 isselected in such a way that the desired circle diameter dr results fromdistance Z1 a from the axicon to the collimating lens 12, which is equalto f′. The desired width br of the ring can be adjusted via the distanceZ1 b (collimating lens 12 to focusing lens 11). As a matter of puregeometry, the small width of the circular illumination leads to a shortfocal line. A minimum can be achieved at distance f′.

The optical assembly 6 depicted in FIG. 6 is thus based on the onedepicted in FIG. 5A so that only the differences are described below.The collimating lens 12, here also designed as a plano-convex lens (withits curvature towards the beam direction) is additionally placedcentrally in the beam path between axicon 10 (with its apex towards thebeam direction), on the one side, and the plano-convex lens 11, on theother side. The distance of collimating lens 12 from axicon 10 isreferred to as Z1 a, the distance of focusing lens 11 from collimatinglens 12 as Z1 b, and the distance of the focal line 2 b from thefocusing lens 11 as Z2 (always viewed in beam direction). As shown inFIG. 6, the circular radiation SR formed by axicon 10, which is incidentdivergently and under the circle diameter dr on the collimating lens 12,is adjusted to the required circle width br along the distance Z1 b foran at least approximately constant circle diameter dr at the focusinglens 11. In the case shown, a very short focal line 2 b is intended tobe generated so that the circle width br of approximately 4 mm at lens12 is reduced to approximately 0.5 mm at lens 11 due to the focusingproperties of lens 12 (circle diameter dr is 22 mm in the example).

In the depicted example, it is possible to achieve a length of the focalline 1 of less than 0.5 mm using a typical laser beam diameter of 2 mm,a focusing lens 11 with a focal length f=25 mm, and a collimating lenswith a focal length f′=150 mm, and choosing Z1 a=Z1 b=140 mm and Z2=15mm.

Once the fault lines are created, separation can occur via: 1) manual ormechanical stress on or around the fault line; the stress or pressureshould create tension that pulls both sides of the fault line apart tobreak the areas that are still bonded together; 2) using a heat sourceto create a thermal stress zone around the fault line to put the defectline in tension and induce partial or total separation along the faultline; and 3) using an ion exchange process to introduce stress in theregion around the fault line. Additionally, the use of the picosecondlaser process on either non-chamfered edges or incompletely chamferededges, but that have “sacrificial” regions that control damage caused byedge impact is described below.

The second method takes advantage of an existing edge to create achamfer by applying a focused (typically CO₂) laser very close to theintersection between the surfaces of the edge and substrate. The laserbeam must be highly absorbed by the substrate material to create atemperature gradient that spans the interval extending from thematerial's melting temperature down to its strain point. This thermalgradient generates a stress profile that results in separation orpeeling of a very thin strip of the material. The thin strip of materialcurls and peels off from the bulk of the material and has dimensionsdetermined by the depth of the region defined between the strain andsoftening zones. This method can be combined with the previous method topeel the thin strip of material off at planes dictated by the faultlines. In this embodiment, the thermal gradient is established in thevicinity of the fault line. The combination of thermal gradient andfault line can yield better control of the chamfer edge shape andsurface texture than would otherwise be possible by using purely thermalmeans.

FIG. 7A gives an overview of the processes described in the presentapplication.

One method relies on induced nonlinear absorption to create fault linesas described hereinabove for forming the desired shapes of parts andedges using a short-pulse laser. The process relies on the materialtransparency to the laser wavelength in the linear regime (low laserintensity), which provides high surface and edge quality with reducedsubsurface damage created by the area of high intensity around the laserfocus. One of the key enablers of this process is the high aspect ratioof the defect line created by the ultra-short pulsed laser. It allowscreation of a fault line with long and deep defect line that can extendfrom the top to the bottom surfaces of the material to be cut andchamfered. In principle, each defect line (perforation) can be createdby a single pulse and if desired, additional pulses can be used toincrease the extension of the affected area (depth and width).

Using the same principle illustrated in FIGS. 1A-1C to separate a glasssubstrate with flat edges, the process to produce chamfered edges can bemodified as illustrated in FIG. 7B. To separate and form a chamferededge, three separate planes of defect lines that intersect and definethe boundaries of the desired edge shape can be formed in the material.Different shapes can be created by using just two intersecting defectline planes as illustrated in FIG. 7C, but the interior flat part of theedge may need to be broken or separated without any defect lines (e.g.through mechanical or thermal means).

Laser and Optical System

For the purpose of cutting glass or other transparent brittle materials,a process was developed that uses a 1064 nm picosecond laser incombination with line-focus beam forming optics to create defect linesin substrates. A sample Corning® Gorilla® Glass code 2320 substrate with0.7 mm thickness was positioned so that it was within the line-focus.With a line-focus of ˜1 mm extension, and a picosecond laser thatproduces output power of >30 W at a repetition rate of 200 kHz (˜150μJ/pulse), then the optical intensities in the line region can easily behigh enough to create non-linear absorption in the material. A region ofdamaged, ablated, vaporized, or otherwise modified material is createdthat approximately follows the linear region of high intensity.

Note that the typical operation of such a picosecond laser creates a“burst” of pulses. Each “burst” may contain multiple sub-pulses of veryshort duration (˜10 psec). Each sub-pulse is separated in time byapproximately 20 nsec (50 MHz), with the time often governed by thelaser cavity design. The time between each “burst” will be much longer,often ˜5 μsec, for a laser repetition rate of ˜200 kHz. The exacttimings, pulse durations, and repetition rates can vary depending on thelaser design. But short pulses (<15 psec) of high intensity have beenshown to work well with this technique.

More specifically, as illustrated in FIGS. 8A and 8B, according toselected embodiments described herein, the picosecond laser creates a“burst” 500 of pulses 500A, sometimes also called a “burst pulse”.Bursting is a type of laser operation where the emission of pulses isnot in a uniform and steady stream but rather in tight clusters ofpulses [See reference]. Each “burst” 500 may contain multiple pulses500A (such as 2 pulses, 3 pulses, 4 pulses, 5 pulses, 10, 15, 20, ormore) of very short duration T_(d) up to 100 psec (for example, 0.1psec, 5 psec, 10 psec, 15 psec, 18psec, 20 psec, 22 psec, 25 psec, 30psec, 50 psec, 75 psec, or therebetween). The pulse duration isgenerally in a range from about 1 psec to about 1000 psec, or in a rangefrom about 1 psec to about 100 psec, or in a range from about 2 psec toabout 50 psec, or in a range from about 5 psec to about 20 psec. Theseindividual pulses 500A within a single burst 500 can also be termed“sub-pulses,” which simply denotes the fact that they occur within asingle burst of pulses. The energy or intensity of each laser pulse 500Awithin the burst may not be equal to that of other pulses within theburst, and the intensity distribution of the multiple pulses within aburst 500 may follow an exponential decay in time governed by the laserdesign. Preferably, each pulse 500A within the burst 500 of theexemplary embodiments described herein are separated in time from thesubsequent pulse in the burst by a duration T_(p) from 1 nsec to 50 nsec(e.g. 10-50 nsec, or 10-40 nsec, or 10-30 nsec, with the time oftengoverned by the laser cavity design. For a given laser, the timeseparation T_(p) between each pulses (pulse-to-pulse separation) withina burst 500 is relatively uniform (±10%). For example, in someembodiments, each pulse is separated in time from the subsequent pulseby approximately 20 nsec (50 MHz pulse repetition frequency). Forexample, for a laser that produces pulse-to-pulse separation T_(p) ofabout 20 nsec, the pulse-to-pulse separation T_(p) within a burst ismaintained within about ±10%, or is about ±2 nsec. The time between each“burst” (i.e., time separation T_(b) between bursts) will be much longer(e.g., 0.25≦T_(b)≦1000 microseconds, for example 1-10 microseconds, or3-8 microseconds,) For example in some of the exemplary embodiments ofthe laser described herein it is around 5 microseconds for a laserrepetition rate or frequency of about 200 kHz. The laser repetition rateis also referred to as burst repetition frequency or burst repetitionrate herein, and is defined as the time between the first pulse in aburst to the first pulse in the subsequent burst. In other embodiments,the burst repetition frequency is in a range of between about 1 kHz andabout 4 MHz, or in a range between about 1 kHz and about 2 MHz, or in arange of between about 1 kHz and about 650 kHz, or in a range of betweenabout 10 kHz and about 650 kHz. The time T_(b) between the first pulsein each burst to the first pulse in the subsequent burst may be 0.25microsecond (4 MHz burst repetition rate) to 1000 microseconds (1 kHzburst repetition rate), for example 0.5 microseconds (2 MHz burstrepetition rate) to 40 microseconds (25 kHz burst repetition rate), or 2microseconds (500 kHz burst repetition rate) to 20 microseconds (50 kHzburst repetition rate). The exact timings, pulse durations, andrepetition rates can vary depending on the laser design anduser-controllable operating parameters. Short pulses (T_(d)<20 psec andpreferably T_(d)≦15 psec) of high intensity have been shown to workwell.

The required energy to modify the material can be described in terms ofthe burst energy—the energy contained within a burst (each burst 500contains a series of pulses 500A), or in terms of the energy containedwithin a single laser pulse (many of which may comprise a burst). Forthese applications, the energy per burst (per millimeter of the materialto be cut) can be from 10-2500 μJ, or from 20-1500 μJ, or from 25-750μJ, or from 40-2500 μJ, or from 100-1500 μJ, or from 200-1250 μJ, orfrom 250-1500 μJ, or from 250-750 μJ. The energy of an individual pulsewithin the burst will be less, and the exact individual laser pulseenergy will depend on the number of pulses 500A within the burst 500 andthe rate of decay (e.g, exponential decay rate) of the laser pulses withtime as shown in FIGS. 8A and 8B. For example, for a constantenergy/burst, if a pulse burst contains 10 individual laser pulses 500A,then each individual laser pulse 500A will contain less energy than ifthe same burst pulse 500 had only 2 individual laser pulses.

The use of lasers capable of generating such pulse bursts isadvantageous for cutting or modifying transparent materials, for exampleglass. In contrast with the use of single pulses spaced apart in time bythe repetition rate of a single-pulsed laser, the use of a burst pulsesequence that spreads the laser energy over a rapid sequence of pulseswithin burst 500 allows access to larger timescales of high intensityinteraction with the material than is possible with single-pulse lasers.While a single-pulse can be expanded in time, conservation of energydictates that as this is done, the intensity within the pulse must dropas roughly one over the pulse width. Hence if a 10 psec single pulse isexpanded to a 10 nsec pulse, the intensity drops by roughly three ordersof magnitude. Such a reduction can reduce the optical intensity to thepoint where non-linear absorption is no longer significant and thelight-material interaction is no longer strong enough to allow forcutting. In contrast, with a burst pulse laser, the intensity duringeach pulse or sub-pulse 500A within the burst 500 can remain veryhigh—for example three pulses 500A with pulse duration T_(d) 10 psecthat are spaced apart in time by a separation T_(p) of approximately 10nsec still allows the intensity within each pulse to be approximatelythree times higher than that of a single 10 psec pulse, while the laseris allowed to interact with the material over a timescale that is threeorders of magnitude larger. This adjustment of multiple pulses 500Awithin a burst thus allows manipulation of timescale of thelaser-material interaction in ways that can facilitate greater or lesserlight interaction with a pre-existing plasma plume, greater or lesserlight-material interaction with atoms and molecules that have beenpre-excited by an initial or previous laser pulse, and greater or lesserheating effects within the material that can promote the controlledgrowth of defect lines (perforations). The amount of burst energyrequired to modify the material will depend on the substrate materialcomposition and the length of the line focus used to interact with thesubstrate. The longer the interaction region, the more the energy isspread out, and the higher the burst energy that will be required.)

A defect line or a hole is formed in the material when a single burst ofpulses strikes essentially the same location on the glass. That is,multiple laser pulses within a single burst can produce a single defectline or a hole location in the glass. Of course, if the glass istranslated (for example by a constantly moving stage) or the beam ismoved relative to the glass, the individual pulses within the burstcannot be at exactly the same spatial location on the glass. However,they are well within 1 μm of one another-i.e., they strike the glass atessentially the same location. For example, they may strike the glass ata spacing sp where 0<sp≦500 nm from one another. For example, when aglass location is hit with a burst of 20 pulses the individual pulseswithin the burst strike the glass within 250 nm of each other. Thus, insome embodiments 1 nm<sp<250 nm. In in some embodiments 1 nm<sp<100 nm.

Hole or Damage Track Formation

If the substrate has sufficient stress (e.g. with ion exchanged glass),then the part will spontaneously separate along the fault line tracedout by the laser process. However, if there is not a lot of stressinherent to the substrate, then the picosecond laser will simply formdefect lines in the substrate. These defect lines may take the form ofholes with interior dimensions (diameters) ˜0.5-1.5 μm.

The holes or defect lines may or may not perforate the entire thicknessof the material, and may or may not be a continuous opening throughoutthe depth of the material. FIG. 1C shows an example of such tracksperforating the entire thickness of a piece of 700 μm thickunstrengthened Gorilla® Glass substrate. The perforations or damagetracks are observed through the side of a cleaved edge. The tracksthrough the material are not necessarily through holes—there may beregions of glass that plug the holes, but they are generally small insize.

Note that upon separation at the fault line, fracture occurs along thedefect lines to provide a part or edge having a surface with featuresderived from the defect lines. Before separation, the defect lines aregenerally cylindrical in shape. Upon separation, the defect linesfracture and remnants of the defect lines are evident in the contours ofthe surface of the separated part or edge. In an ideal model, the defectlines are cleaved in half upon separation so that the surface of theseparated part or edge includes serrations corresponding tohalf-cylinders. In practice, separation may deviate from an ideal modeland the serrations of the surface may be an arbitrary fraction of theshape of the original defect line. Irrespective of the particular form,features of the separated surface will be referred to as defect lines toindicate the origin of their existence.

The lateral spacing (pitch) between the defect lines is determined bythe pulse rate of the laser as the substrate is translated underneaththe focused laser beam. Only a single picosecond laser pulse or burst isnecessary to form an entire hole, although multiple pulses or bursts maybe used if desired. To form defect lines at different pitches, the lasercan be triggered to fire at longer or shorter intervals. For cuttingoperations, the laser triggering generally is synchronized with thestage driven motion of the part beneath the beam, so laser pulses aretriggered at a fixed interval, such as every 1 μm, or every 5 μm. Theexact spacing between adjacent defect lines is determined by thematerial properties that facilitate crack propagation from perforationto perforation, given the stress level in the substrate. Instead ofcutting a substrate, it is also possible to use the same method to onlyperforate the material. In this case, the defect lines may be separatedby larger spacings (e.g. 5 μm pitch or greater).

The laser power and lens focal length (which determines the focal linelength and hence power density) are particularly important to ensurefull penetration of the glass and low surface and sub-surface damage.

In general, the higher the available laser power, the faster thematerial can be cut with the above process. The process(s) disclosedherein can cut glass at a cutting speed of 0.25 msec, or faster. A cutspeed (or cutting speed) is the rate the laser beam moves relative tothe surface of the substrate material (e.g., glass) while creatingmultiple defect lines holes. High cut speeds, such as, for example 400mm/sec, 500 mm/sec, 750 mm/sec, 1 msec, 1.2 msec, 1.5 msec, or 2 msec,or even 3.4 msec to 4 msec are often desired in order to minimizecapital investment for manufacturing, and to optimize equipmentutilization rate. The laser power is equal to the burst energymultiplied by the burst repetition frequency (rate) of the laser. Ingeneral, to cut glass materials at high cutting speeds, the defect linesare typically spaced apart by 1-25 μm, in some embodiments the spacingis preferably 3 μm or larger—for example 3-12 μm, or for example 5-10μm.

For example, to achieve a linear cutting speed of 300 mm/sec, 3 μm holepitch corresponds to a pulse burst laser with at least 100 kHz burstrepetition rate. For a 600 mm/sec cutting speed, a 3 μm pitchcorresponds to a burst-pulsed laser with at least 200 kHz burstrepetition rate. A pulse burst laser that produces at least 40 μJ/burstat 200 kHz, and cuts at a 600 mm/s cutting speed needs to have a laserpower of at least 8 Watts. Higher cut speeds require accordingly higherlaser powers.

For example, a 0.4 msec cut speed at 3 μm pitch and 40 μJ/burst wouldrequire at least a 5 W laser, a 0.5 msec cut speed at 3 μm pitch and 40μJ/burst would require at least a 6 W laser. Thus, preferably the laserpower of the pulse burst ps laser is 6 W or higher, more preferably atleast 8 W or higher, and even more preferably at least 10 W or higher.For example, in order to achieve a 0.4 msec cut speed at 4 μm pitch(defect line spacing, or damage tracks spacing) and 100 μJ/burst, onewould require at least a 10 W laser, and to achieve a 0.5 msec cut speedat 4 μm pitch and 100 μJ/burst, one would require at least a 12 W laser.For example, a to achieve a cut speed of 1 m/sec at 3 μm pitch and 40μJ/burst, one would require at least a 13 W laser. Also, for example, 1m/sec cut speed at 4 μm pitch and 400 μJ/burst would require at least a100 W laser.

The optimal pitch between defect lines (damage tracks) and the exactburst energy is material dependent and can be determined empirically.However, it should be noted that raising the laser pulse energy ormaking the damage tracks at a closer pitch are not conditions thatalways make the substrate material separate better or with improved edgequality. A pitch that is too small (for example <0.1 micron, or in someexemplary embodiments <1 μm, or in other embodiments <2 μm) betweendefect lines (damage tracks) can sometimes inhibit the formation ofnearby subsequent defect lines (damage tracks), and often can inhibitthe separation of the material around the perforated contour. Anincrease in unwanted micro cracking within the glass may also result ifthe pitch is too small. A pitch that is too long (e.g. >50 μm, and insome glasses >25 μm or even >20 μm) may result in “uncontrolledmicrocracking”—i.e., where instead of propagating from defect line todefect line along the intended contour, the microcracks propagate alonga different path, and cause the glass to crack in a different(undesirable) direction away from the intended contour. This mayultimately lower the strength of the separated part since the residualmicrocracks constitute flaws that weaken the glass. A burst energy forforming defect lines that is too high (e.g., >2500 μJ/burst, and in someembodiments >500 μJ/burst) can cause “healing” or re-melting ofpreviously formed defect lines, which may inhibit separation of theglass. Accordingly, it is preferred that the burst energy be <2500μJ/burst, for example, <500 μJ/burst. Also, using a burst energy that istoo high can cause formation of microcracks that are extremely large andcreate structural imperfections that can reduce the edge strength of thepart after separation. A burst energy that is too low (e.g. <40μJ/burst) may result in no appreciable formation of defect lines withinthe glass, and hence may necessitate especially high separation force orresult in a complete inability to separate along the perforated contour.

Typical exemplary cutting rates (speeds) enabled by this process are,for example, 0.25 m/sec and higher. In some embodiments, the cuttingrates are at least 300 mm/sec. In some embodiments, the cutting ratesare at least 400 mm/sec, for example, 500 mm/sec to 2000 mm/sec, orhigher. In some embodiments the picosecond (ps) laser utilizes pulsebursts to produce defect lines with periodicity between 0.5 μm and 13μm, e.g. between 0.5 and 3 μm. In some embodiments, the pulsed laser haslaser power of 10 W-100 W and the material and/or the laser beam aretranslated relative to one another at a rate of at least 0.25 m/sec; forexample, at the rate of 0.25 m/sec to 0.35 m/sec, or 0.4 m/sec to 5m/sec. Preferably, each pulse burst of the pulsed laser beam has anaverage laser energy measured at the workpiece greater than 40 μJ perburst per mm thickness of workpiece. Preferably, each pulse burst of thepulsed laser beam has an average laser energy measured at the workpiecegreater of less than 2500 μJ per burst per mm thickness of workpiece,and preferably lass than about 2000 μJ per burst per mm thickness ofworkpiece, and in some embodiments less than 1500 μJ per burst per mmthickness of workpiece; for example, not more than 500 μJ per burst permm thickness of workpiece.

We discovered that much higher (5 to 10 times higher) volumetric pulseenergy density (μJ/μm³) is required for perforating alkaline earthboroaluminosilicate glasses with low or no alkali content. This can beachieved, for example, by utilizing pulse burst lasers, preferably withat least 2 pulses per burst and providing volumetric energy densitieswithin the alkaline earth boroaluminosilicate glasses (with low or noalkali) of about 0.050/μJ/μm³ or higher, e.g., at least 0.1 μJ/μm³, forexample 0.1-0.5 μJ/μm³.

Accordingly, it is preferable that the laser produces pulse bursts withat least 2 pulses per burst. For example, in some embodiments the pulsedlaser has a power of 10 W-150 W (e.g., 10 W-100 W) and produces pulsebursts with at least 2 pulses per burst (e.g., 2-25 pulses per burst).In some embodiments the pulsed laser has a power of 25 W-60 W, andproduces pulse bursts with at least 2-25 pulses per burst, andperiodicity or distance between the adjacent defect lines produced bythe laser bursts is 2-10 μm. In some embodiments, the pulsed laser has apower of 10 W-100 W, produces pulse bursts with at least 2 pulses perburst, and the workpiece and the laser beam are translated relative toone another at a rate of at least 0.25 m/sec. In some embodiments theworkpiece and/or the laser beam are translated relative to one anotherat a rate of at least 0.4 m/sec.

For example, for cutting 0.7 mm thick non-ion exchanged Corning code2319 or code 2320 Gorilla® glass, it is observed that pitches of 3-7 μmcan work well, with pulse burst energies of about 150-250 μJ/burst, andburst pulse numbers that range from 2-15, and preferably with pitches of3-5 μm and burst pulse numbers (number of pulses per burst) of 2-5.

At 1 m/sec cut speeds, the cutting of Eagle XG® glass typically requiresutilization of laser powers of 15-84 W, with 30-45 W often beingsufficient. In general, across a variety of glass and other transparentmaterials, applicants discovered that laser powers between 10 W and 100W are preferred to achieve cutting speeds from 0.2-1 m/sec, with laserpowers of 25-60 W being sufficient (or optimum) for many glasses. Forcutting speeds of 0.4 msec to 5 msec, laser powers should preferably be10 W-150 W, with burst energy of 40-750 μJ/burst, 2-25 bursts per pulse(depending on the material that is cut), and defect line separation(pitch) of 3 to 15 μm, or 3-10 μm. The use of picosecond pulse burstlasers would be preferable for these cutting speeds because theygenerate high power and the required number of pulses per burst. Thus,according to some exemplary embodiments, the pulsed laser produces 10W-100 W of power, for example 25 W to 60 W, and produces pulse bursts atleast 2-25 pulses per burst and the distance between the defect lines is2-15 μm; and the laser beam and/or workpiece are translated relative toone another at a rate of at least 0.25 msec, in some embodiments atleast 0.4 msec, for example 0.5 msec to 5 msec, or faster.

Cutting and Separating Chamfered Edges Chamfer Method 1

Different conditions were found that allow the separation of chamferededges using unstrengthened Gorilla® Glass, specifically Corning code2320. The first method is to use the picosecond laser to create defectlines to form a fault line consistent with the desired shape (in thiscase a chamfered edge). After this step, mechanical separation can beaccomplished by using a breaking plier, manually bending the part, orany method that creates tension that initiates and propagates theseparation along the fault line. To create chamfered edges with defectlines in 700 μm thick unstrengthened Gorilla® Glass and mechanicallyseparate the parts, the best results were found for the following opticsand laser parameters:

Picosecond Laser (1064 nm)

Input beam diameter to axicon lens ˜2 mm

Axicon angle=10 degrees

Initial collimating lens focal length=125 mm

Final objective lens focal length=40 mm

Focus set to be at Z=0.7 mm (i.e. line focus set to be centered withregard to the glass thickness)

Laser power at 100% of full power (˜40 Watts)

Burst repetition rate of the laser=200 kHz.

Energy per burst=200 μJ (40 W/200 kHz)

Pitch=5 μm

3 pulses/burst

Single pass per defect line

An alternative method of achieving separation is to use a relativelydefocused CO₂ laser beam (˜2 mm spot diameter) that follows thepicosecond laser step after the picosecond laser has finished tracingthe desired contour. The thermal stress induced by the CO₂ laser isenough to initiate and propagate the separation or shaping of the edgealong the desired contour. For this case, the best results were foundfor the following optics and laser parameters:

Picosecond Laser (1064 nm)

Input beam diameter to axicon lens ˜2 mm

Axicon angle=10 degrees

Initial collimating lens focal length=125 mm

Final objective lens focal length=40 mm

Focus set to be at Z=0.7 mm (i.e. line focus set to be centered withregard to the glass thickness)

Laser power at 75% of full power (˜30 Watts)

Burst repetition rate of the laser=200 kHz.

3 pulses/burst

Energy per burst =150 μJ (30 W/200 kHz)

Pitch=5 μm

Single pass

CO₂ Laser

Laser is a 200 W full power laser

Laser translation speed: 10 m/min

Laser power=100%

Pulse duration 17 μs

Laser modulation frequency 20 kHz

Laser duty cycle=17/50 μs=34% duty (about 68 Watt output).

Laser beam defocus (relative to the incident surface of the glass)=20 mm

Chamfer Method 2 Method 2A

A second chamfering method takes advantage of an existing edge to createa chamfer by applying a highly-focused CO₂ laser very close to theintersection between the surfaces of the edge and substrate. In contrastto the CO₂ laser conditions described above, in this case the size ofthe focused CO₂ beam at the substrate surface is ˜100 μm diameter, whichallows the beam to heat the glass locally to much higher temperaturesthan the defocused beam described in Method 1. The laser must be highlyabsorbed by the substrate material to create an intense thermal gradientthat spans the temperature range from the material's melting temperaturedown to the material's strain point. The thermal gradient generates astress profile that induces separation or peeling of a very thin stripof the material that curls and peels off from the bulk of the material.The dimensions of the thin strip are determined by the depth of theregion in the material having temperatures between the strain andsoftening points.

This method can be combined with the previous method to peel off at theplanes dictated by the fault lines. In other words, a picosecond lasercan be employed as described hereinabove to form a fault line having ashape consistent with the desired shape or contour of the edge and athermal gradient can be established in and around the fault line toprompt release of the thin strip of material. In this embodiment, thefault lines produced by the picosecond laser guide the direction ofcurling or peeling of the thin strip of material and finer control ofthe shape or contour of the edge may be achieved.

As illustrated in FIG. 9, the second method relies on the absorption bythe substrate of the laser wavelength (e.g., a CO₂ at 10.6 μm).Absorption of the laser by the material leads to the establishment of athermal gradient that encompasses temperatures that extend from at leastthe strain point of the material to at least the softening point of thematerial. As shown in FIG. 10, a strip of glass separates from the bulkof the substrate to form a curled peel when such a thermal gradient iscreated. When the laser is tightly focused near the edge (e.g. within<100 μm from the edge) as shown in FIG. 9, a strip of curled glass ispeeled from the right angle corner and forms a chamfer that is generallyconcave as shown in FIG. 10. To chamfer both corners, the sample can beflipped over and the process can be repeated on the second corner. Asshown in FIG. 10, the defect lines of the flat portion of the edge showa texture consistent with that shown in FIG. 1C for a flat edge formedby through-hole perforations. FIG. 12 shows that by changing thechamfering speed (defined as the CO₂ beam scan speed), it is possible tochange the characteristics of the chamfered edges: chamfer angle, widthof the flat face (A) or height/width (B/C). By changing the CO₂ laserscan speed, the rate of laser energy deposition onto the material variesand the characteristics of the thermal gradient (e.g. spatial extent,temperature range) are changed. By moving the laser faster, the faultline becomes shallower and the strip of material that peels becomesnarrower and shallower. The chamfering speed was varied from 3 m/min to10 m/min in the examples shown in FIG. 12. The CO₂ laser had a peakpower of 200 W and was set to a repetition rate of 30 kHz with a pulsewidth of 2.9 μs, which created a CO₂ output power governed by the 9%duty cycle of ˜18 W.

CO₂ Laser Conditions for Peel

Laser is a 200 W full power laser

Laser translation speed: 3 m/min (50 mm/s)

Laser power=100%

Pulse duration 2.9 μs

Laser modulation frequency 30 kHz

Laser duty cycle=2.9/33 μs=9% duty (about 18 W output).

Laser beam defocus=0.7 mm

Method 2B

In this example, the picosecond perforation portion of Chamfer Method 1was combined with the thermal peeling of Chamfer Method 2A to create acontrolled peeling with separation guided by the defect line planes. Asshown in FIGS. 11A and 11B, peeling of the right angle corners occurs.Peeling and detachment may not, however, occur entirely along the defectplane because the thermal gradient in the softening zone provides asecondary driving force that may influence the path of detachment.Depending on the relative position between the defect plane and thecracking line defined by the thermal gradient, separation may occur to agreater or lesser extent along the fault line. FIG. 11B illustrates anexample in which a portion of the peeling path deviates from the pathdefined by the defect lines. The deviation is most pronounced along theflat portion of the edge. It should be possible, however, to separatethe corner at the defect line plane with the proper combination ofdefect line characteristics and proper heating with the CO₂ laser.

Sacrificial Edges

Even if the peeled glass does not entirely follow the defect line plane,the presence of the residual defect line inside the glass can bebeneficial because it may arrest the propagation of cracks that formwhen the edge is impacted. In this case, the residual interior defectline planes can be used to serve as damage arrest locations, in effectcreating a “sacrificial” edge part of the region of substrate materialthat is on the surface side of the residual interior defect lines. Infact, creation of sacrificial edges that include a residual interiordefect line on the interior side of the separated edge (or a set ofresidual interior defect lines that intersect to form a more complexinterior bevel inside of the true edge), may be a method of improvingthe reliability of the chamfered part without the need for a physicalchamfer feature on the outside edge of the part and without themechanical grinding and polishing needed to create that feature. Someoptions for this type of sacrificial edge are shown in FIG. 13. Sincethe picosecond laser process described above creates each defect line ina single pass and at speeds of up to 1 m/s, it is very easy andcost-effective to create extra “damage stop” lines. When subjected tostress, for example an impacting force, the glass will separate alongthe sacrificial edge and prevent cracks from the impact from propagatinginto the interior of the part, thus leaving the balance of the partintact.

Chamfer Method 3

Finally, separation of the outside glass edge pieces formed by thedefect lines need not be done by application of the CO₂ laser orapplication of mechanical force. In many instances, the glass partseparated from a glass substrate is sent for chemical strengthening inan ion exchange process. Ion exchange itself can create enough stress toprompt peeling or separation at the chamfer regions or corners of thepart. The introduction of new ions into the glass surface can createenough stress to cause the outside corner pieces to peel or separate. Inaddition, the high temperature salt bath used in the ion exchangeprocess can provide thermal stress sufficient to induce peeling orseparation along the fault line to provide a chamfered or otherwiseshaped edge. In either case, the ultimate result is an edge that moreclosely follows the interior defect lines to form the desired chamfershape see FIG. 14).

Additionally or alternatively, etching of the part in an acid solution(e.g., a solution of 1.5 M HF and 0.9 M H₂SO₄) can create enough stressto cause the outside corner pieces to peel or separate.

The chambering methods described herein can also be applied to Corning®Eagle XG® (with the exception of the methods including ion exchange)glass as described in application entitled Laser Cutting of DisplayGlass Compositions(U.S. Provisional Patent Application Ser. No.62/023471).

The methods described above provide the following benefits that maytranslate to enhanced laser processing capabilities and cost savings andthus lower cost manufacturing. In the current embodiment, the cuttingand chamfering processes offer:

Chamfering or fully cutting parts with chamfered edges: the disclosedmethod is capable of completely separating/cutting Gorilla® Glass andother types of transparent glasses (strengthened or unstrengthened) in aclean and controlled fashion. Full separation and/or edge chamferingwere demonstrated using several methods. With Chamfer Method 1, the partis cut to size or separated from glass matrix with a chamfered edge and,in principle, no further post processing is required. With ChamferMethod 2, the part is already cut to size with pre-existing flat edgesand the laser is used to chamfer the edges.

Reduced subsurface defects: with Chamfer Method 1, due to theultra-short pulse interaction between laser and material, there islittle thermal interaction and thus a minimal heat affected zone thatcan result in undesirable stress and micro-cracking. In addition, theoptics that condenses the laser beam into the glass creates defect linesthat are typically 2 to 5 microns diameter on the surface of the part.After separation, the subsurface damage can be as low as <30 μm. Thishas great impact on the edge strength of the part and reduces the needto further grind and polish the edges, as these subsurface damages cangrow and evolve into micro-cracks when the part is submitted to tensilestress and weaken the strength of the edge.

Process cleanliness: Chamfer Method 1 is capable of chamfering glass ina clean and controlled fashion. It is very problematic to useconventional ablative processes for chamfering because they generate alot of debris. Such ablation-generated debris is problematic, because itcan be hard to remove even with various cleaning and washing protocols.Any adhered particulates can cause defects for later processes where theglass is coated or metalized to create thin film transistors, etc. Thecharacteristics of the laser pulses and the induced interactions withthe material of the disclosed method avoid this issue because they occurin a very short time scale and the material transparency to the laserradiation minimizes the induced thermal effects. Since the defect lineis created within the object, the presence of debris and adheredparticles during the cutting step is virtually eliminated. If there areany particulates resulting from the created defect line, they are wellcontained until the part is separated.

Elimination of Process Steps

The process to fabricate glass plates from the incoming glass panel tothe final size and shape involves several steps that encompass cuttingthe panel, cutting to size, finishing and edge shaping, thinning theparts down to their target thickness, polishing, and even chemicallystrengthening in some cases. Elimination of any of these steps willimprove manufacturing cost in terms of process time and capital expense.The presented method may reduce the number of steps by, for example:

-   Reduced debris and edge defects generation—potential elimination of    washing and drying stations-   Cutting the sample directly to its final size with shaped edges,    shape and thickness—reducing or eliminating need for mechanical    finishing lines and a huge non-value added cost associated with    them.

The relevant teachings of all patents, published applications andreferences cited herein are incorporated by reference in their entirety.

While exemplary embodiments have been described herein, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the scope of theinvention encompassed by the appended claims.

What is claimed is:
 1. A glass article including at least one chamferededge having a plurality of defect lines extending at least 250 μm, thedefect lines each having a diameter less than or equal to about 5μm. 2.The glass article of claim 1, wherein the glass article compriseschemically strengthened glass.
 3. The glass article of claim 1, whereinthe glass article comprises non-strengthened glass.
 4. The glass articleof claim 1, wherein the chamfered edge has an Ra surface roughness lessthan about 0.5 μm.
 5. The glass article of claim 1, wherein thechamfered edge has subsurface damage up to a depth less than or equal toabout 75 μm.